Wafer shipping box and a lower retaining member thereof

A wafer shipping box includes a case and a positioning unit. The case includes a base, a cover, and a receiving space defined by the base and the cover. The positioning unit is disposed in the receiving space and includes a lower retaining member connected to the base, an upper retaining member connected to the cover, and a cassette disposed therebetween. The cassette includes two upright holding walls spaced apart from each other, each of which has a plurality of lateral confining slots aligned in a front-rear direction. The lower retaining member is formed with a plurality of lower confining slots, each of which is defined by two slot walls interconnected at bottom ends thereof to form a slot bottom. The slot bottoms are respectively misaligned from central positions of the lateral confining slots along the front-rear direction.